Top tier:
Orijen/Acana
Blue Wilderness
Wellness Core
Taste of the Wild
If cost becomes an issue, The Tractor Supply house brand 4Health is made by Diamond and is pretty good quality, and I think about $37 for the big bag if you get the grain-free variety. It's good middle of the road food, is lacking a lot of the fillers and trash that Wal-Mart food has, and unless you're feeding a herd, it doesn't cost much more than the generic corn chunks. The grain-free is in the dark brown bags.
Vets and kennels often learn about nutrition from pet food sales reps, and push the Nestle brands (like Science Diet, which is junk) for that reason. Stay away from any of Nestle's brands and anything from Wal-Mart.
You can really judge any food yourself. The first few ingredients should be specific meats. Avoid anything with soy, corn, grains, or anything labeled by-product. A higher percentage of protein is usually good as long as it isn't from soy or another plant.